Synthesis of ternary nitrides by mechanochemical alloying

Abstract

Ternary metal nitrides (of general formula M_xM′_yN_z) attract considerable interest because of their special mechanical, electrical, magnetic, and catalytic properties. Usually they are prepared by ammonolysis of ternary oxides (M_xM′_yO_m) at elevated temperatures. We show that ternary transition metal nitrides are also obtained by nitridation of the corresponding ternary carbide at 823 K. This transformation appears to occur by solid-state diffusion of carbide and nitride ions. To establish more general synthesis schemes for ternary nitrides, we have focused on the preparation of ternary nitrides by mechanochemical alloying of a binary transition metal nitride (M_xN) with an elemental transition metal. In this way, we have been able to prepare Fe₃Mo₃N and Co₃Mo₃N by ball-milling of Mo₂N with Fe and Co, respectively. The transformation sequence from the starting materials (the binary nitride and the transition metal) to the ternary nitride was followed by Mössbauer spectroscopy (for Fe₃Mo₃N) and by X-ray powder diffraction (for both Fe₃Mo₃N and Co₃Mo₃N). Usually, the preparation of a given ternary nitride by ammonolysis of a ternary oxide is dependent on the availability of an oxide precursor with the desired stoichiometric ratio of the two metals. In the present mechanochemical approach, this is not a prerequisite. These synthesis routes are expected to be applicable to the synthesis of a wide range of ternary compounds.